Prosecutors in the US have accused Venezuela of secretly funding the election campaign of Argentina's newly inaugurated president, Cristina Kirchner. The claim ignited a political row between the three countries.

The prosecutors told a Miami court on Wednesday that a suitcase filled with nearly $800,000 (£392,000) intercepted at Buenos Aires airport was a payment from the government of President Hugo Chávez. Venezuela and Argentina rejected the allegation as a politically motivated smear.

Kirchner, thrown on the defensive on her first week in the job, said it was an example of "garbage in international politics" and that the US wanted to "subordinate" other nations. "This president may be a woman but she's not going to allow herself to be pressured."

The row revives suspicions that Chávez has used Venezuela's oil revenues to sponsor allies to try to forge a Latin American front against the US, which he terms "the empire". If the charges stick they will taint Venezuela and erode the credibility of Argentina's first elected female head of state. Both governments said it was an attempt to drive a wedge between Chávez and the rest of the region.

Venezuela's foreign minister, Nicolás Maduro, said it was a fabricated scandal. "It is a desperate effort by the US government using the judicial branch for a political, psychological, media war against the progressive governments of the continent."

Three Venezuelans and a Uruguayan are charged with failing to register with the US as agents of a foreign power. All were arrested on Tuesday night.